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 When pigeons dream 

  Date:
      June 6, 2023
  Source:
      Ruhr-University Bochum
  Summary:
      Dreams have been considered a hallmark of human sleep for a
      long time.

      Latest findings, however, suggest that when pigeons sleep, they
      might experience visions of flight. Researchers studied brain
      activation patterns in sleeping pigeons, using functional magnetic
      resonance imaging. The study revealed that similar to mammals,
      most of the brain is highly active during REM sleep. However, this
      wake-like state might come at a cost of reduced waste removal from
      the brain.


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FULL STORY
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During sleep, our brain undergoes a complex set of processes to ensure
we wake up feeling refreshed. In humans, the different phases of sleep,
rapid eye movement (REM) and non-REM sleep, are associated with distinct
changes in physiology, brain activity, and cognition. For instance,
during REM sleep, our brain is very active and we experience our most
vivid, bizarre, and emotional dreams. During non-REM sleep, the brain
is metabolically less active and clears out waste products by flushing
cerebral spinal fluid through the brain's ventricles -- the interconnected
chambers that surround the structures of the brain -- and then through the
brain. This process supposedly helps the body to remove harmful protein
deposits from the brain, like those associated with the development of
Alzheimer's disease.

What happens in a pigeon's brain during sleep?  The question of whether
similar processes also take place in birds has remained unresolved until
now. "The last common evolutionary ancestor of birds and mammals dates
back about 315 million years, to the early days of land vertebrates,"
says Professor Onur Gu"ntu"rku"n, head of the Biopsychology Department at
Ruhr University Bochum. "Yet the sleep patterns in birds are remarkably
similar to those in mammals, including both REM and non-REM phases."
To find out what exactly happens when birds sleep, the researchers used
infrared video cameras and functional magnetic resonance imaging (fMRI)
to observe and record the sleeping and wakeful states of 15 pigeons
specially trained to sleep under these experimental conditions.

The video recordings shed light on the sleep phases in the birds. "We
were able to observe whether one or both eyes were open or closed, and
to track eye movements and changes in pupil size through the pigeons'
transparent eyelids during sleep," explains Mehdi Behroozi from the Bochum
team. Simultaneously, the fMRI recordings provided information about
brain activation and the flow of cerebral spinal fluid in the ventricles.

Dreams of flying "During REM sleep, we observed strong activity in brain
regions responsible for visual processing, including in those areas that
analyze the movement of a pigeon's surroundings during flight," says Mehdi
Behroozi. The team also noticed activity in the areas that process signals
from the body, especially from the wings. "Based on these observations,
we think that birds, just like humans, dream during REM sleep, and might
be experiencing flight in their dreams," adds Mehdi Behroozi.

Additionally, the scientists noticed activation of a particular brain area
known as the amygdala during these phases. "This suggests that if birds
experience something similar to our human dreams, pigeons' dreams might
include emotions as well," says Gianina Ungurean from the Avian Sleep
Group at the Max Planck Institute for Biological Intelligence. This
hypothesis is supported by the fact that the birds' pupils contract
rapidly during REM sleep, like they do during courtship or aggressive
behaviors while awake, as recently demonstrated by Gianina Ungurean
and colleagues.

Washing out the day's dust Like in humans, the flow of cerebral
spinal fluid through ventricles increases during non-REM sleep in
pigeons. However, the team discovered for the first time, in any animal,
that the flow diminished dramatically during REM sleep.

"We think that the increased flood of blood into the brain during REM
sleep, which supports the elevated brain activity, might block the
cerebral spinal fluid from moving from the ventricles into the brain,"
explains Niels Rattenborg, head of the Avian Sleep Group. "This suggests
that REM sleep and its functions might come at the expense of waste
removal from the brain."  However, the scientists are also entertaining
the possibility that REM sleep contributes to waste removal in unexpected
ways. "At the onset of REM sleep, the influx of blood increases vessel
diameter. This might force cerebral spinal fluid that entered the space
during non-REM sleep to flow into the brain tissue, and enhance the
outflow of fluids carrying waste products," says Gianina Ungurean.

The researchers speculate that the process of cleaning the brain during
sleep may be especially crucial for birds. Since their brains have a
higher density of neurons in comparison to mammals, the removal of waste
products may require more efficient -- or more frequent -- flushing
cycles. As birds experience more and shorter REM phases during sleep
than mammals, the associated frequent surge of blood might help to keep
their densely packed brains free of harmful waste products.

Tell us about your dreams!  In the future, the team plans to explore REM
sleep's potential role in waste removal. In addition, they are thinking
about ways to learn about the content of a pigeon's dream. "We hope to
train birds to report if and what they just saw upon awakened from REM
sleep. That would be an essential step towards establishing whether they
dream," explains Gianina Ungurean. But even without a detailed dream
analysis, the new findings already help us to better understand the role
of sleep, in birds as well as in humans. They highlight the importance of
sleep in maintaining a healthy brain and preventing cognitive decline --
and they also imply that dreaming has a very long history.

The study was conducted by the Bochum Biopsychology team as well as
researchers from the Max Planck Institute for Biological Intelligence, the
Max Planck Institute for Neurobiology of Behaviour, the Neurophysiology
Department at Ruhr University Bochum and the Universite' Claude Bernard
Lyon.

    * RELATED_TOPICS
          o Plants_&_Animals
                # Animal_Learning_and_Intelligence # Birds # Biology
                # Mice
          o Earth_&_Climate
                # Hazardous_Waste # Oil_Spills # Recycling_and_Waste #
                Environmental_Science
    * RELATED_TERMS
          o Sleep o Sleep_disorder o Pigeon_intelligence o
          Circadian_rhythm o Brain o Neurobiology o Brain_tumor o
          Neocortex_(brain)

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Story Source: Materials provided by Ruhr-University_Bochum. Original
written by Meike Driessen. Note: Content may be edited for style and
length.


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Journal Reference:
   1. Gianina Ungurean, Mehdi Behroozi, Leonard Bo"ger, Xavier Helluy,
   Paul-
      Antoine Libourel, Onur Gu"ntu"rku"n, Niels
      C. Rattenborg. Wide-spread brain activation and reduced CSF flow
      during avian REM sleep. Nature Communications, 2023; 14 (1) DOI:
      10.1038/s41467-023-38669-1
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Link to news story:
https://www.sciencedaily.com/releases/2023/06/230606111728.htm

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